The present invention relates to a power supply device and a power supply system. Specifically, a plurality of power supply devices are connectable to each other in series. Each of the plurality of power supply devices is particularly suitable for charging a storage battery. Further, the power supply system has a configuration in which the plurality of power supply devices are connected in series.
As disclosed in Japanese Patent Publication No. H05-276736, a conventional configuration in which a plurality of power supply devices are connected in series has been known. In this configuration, a reverse flow prevention diode and a diode for bypassing an output current (also referred to as “a bypass diode” below) are externally attached to an output terminal of each power supply device (a DC-DC converter). In addition, the plurality of power supply devices to which these two diodes are externally attached are connected in series to configure a power supply system. As a result, a current (a load current) is output for a load.
According to this configuration, even when any of the power supply devices stops an operation, an output voltage of the power supply device that stops the operation is equal to or less than a forward voltage of the reverse flow prevention diode that is externally attached to the stopped power supply device. Then, the bypass diode that is externally attached to the stopped power supply device shifts to be in an ON state. Therefore, the bypass diode works as a detour and makes the output currents of other power supply devices, which are in operation states, go through the bypass diode. As a result, the plurality of power supply devices can keep supplying the output current to the load.
The power supply system described above, however, has some problems to be solved as discussed below. When the power supply system is configured with the plurality of the power supply devices that are connected in series, the reverse flow prevention diode and the bypass diode need to be separately prepared as many times as the number of power supply devices that are connected in series in the power supply system, and at the same time, need to be externally attached to each of the power supply devices. As a result, the problem of a complex interconnection exists.
In the configuration of this power supply system, when the plurality of the power supply devices are connected in series and are operated, the following state can occur in the power supply device that stops the operation. Electronic parts other than the bypass diode do not generate heat, however, only the bypass diode in which the output current continuously flows generates heat. Therefore, it is necessary to further prevent the generated heat in the bypass diode from occurring.
As disclosed in Japanese Patent Publication No. 2006-210516, a power supply device has a cooling fan that cools electronic parts such as a capacitor and a diode that configures a switching element and a rectifying circuit by forcibly exhausting the generated heat to outside a case in which the electronic parts are assembled. Thus, the cooling fan can be placed inside the power supply device together with the bypass diode.
The power supply device in which the cooling fan is placed together with the bypass diode, however, still has the following problems to be solved. Although it is possible that the electronic parts are cooled by operating the cooling fan while the power supply device is operated, the cooling fan cannot be operated while the power supply device is in a stop operation state. Therefore, as explained above, it is difficult to cool the bypass diode that generates heat in the stop operation state.